import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.IOException;

public class A224_2 {
	private static boolean isPalindrome(String input) {
		int[] letters = new int[26];
		int onlyOneOdd = 0;
		
		input = input.toUpperCase();

		for(int i = 0; i < input.length(); i++) {
			char curLetter = input.charAt(i);
			if(curLetter >= 'A' && curLetter <= 'Z')
				letters[curLetter - 'A']++;
		}

		for(int i = 0; i < letters.length; i++) {
			if(onlyOneOdd > 1)
				return false;
			if(letters[i] % 2 != 0) {
				onlyOneOdd++;
			}
		}
		return true;
	}
	public static String getResult(String input) {
		if(isPalindrome(input))
			return "yes !";
		return "no...";
	}
	public static void main(String[] args) throws IOException {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		String input;
		StringBuffer output = new StringBuffer();
		
		while((input = br.readLine()) != null) {
			output.append(getResult(input));
			output.append("\n");
		}
		
		System.out.print(output);
	}
}